A quantum dot is a semiconductor nanocrystal that is small enough to exhibit quantum mechanical effects. Specifically, a quantum dot's excitons are confined in all three spatial dimensions. The electronic characteristics of a quantum dot are closely related to its size and shape. The band gap in a quantum dot—which, as in all semiconductors, determines the frequency range of light absorbed/emitted—is inversely proportional to its size. Consequently, the color of emitted light shifts from blue to red when the size of the quantum dot is increased. In other words, the larger the quantum dot, the lower the frequency of light emitted. This size-dependent band structure allows the excitation and emission profiles of quantum dots to be highly controllable. Since the size of a quantum dot is determined when it is made, the conductive properties may be precisely tuned. Furthermore, quantum dots can be readily synthetized through organic methods/precursors facilitating low-cost batch preparation.
Quantum dots are particularly significant for optical applications due to their high extinction coefficient and tunable bandgap. Being zero-dimensional, quantum dots have a sharper density of states than higher-dimensional structures. As a result, they have superior transport and optical properties, and are being researched for use in diode lasers, amplifiers, and biological sensors. Additionally, some quantum dots can convert a single photon into multiple hole-electron pairs, making them an attractive alternative semiconductor candidate in solar cell applications.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.